Electrochemical recovery of copper from alloy scrap

Abstract

In the disclosed process, relatively pure copper is efficiently recovered from metallic alloy, scrap or cement, by electrochemical dissolution and deposition (as the relatively pure copper) under special conditions. In a halide solution, in a cell free from oxygen, the contaminated or alloyed copper is transferred from the impure state and separated by means of a substantially one electron process for the copper involved. The process can be operated in a one-fluid, or a two-fluid cell with diaphragm, depending on the composition of alloy or metal to be purified. For instance, in the case of copper-zinc alloys or mixtures, the copper is readily recovered in a one-fluid cell by suitable arrangement. Particularly with more complex alloys or mixtures, however, it can be advantageous to use a two-fluid cell and an intermediate purification stage between direct dissolution and electrodeposition. Concomitant metals may be recovered in either the metallic state or as chemical compounds. The process allows an orderly, effective electrochemical treatment for the recovery of copper in the presence of impurities.

What is claimed is: 
     
       1. A method for electrochemical hydrometallurgical recovery of metallic copper from impure metallic copper, said metod comprising the steps of: a. using said impure metallic copper as the anode in an electrolytic cell containing a cathode, a cathode compartment, an external electrical circuit means for connecting said cathode to the impure metallic copper anode, and anode compartment, an aqueous anolyte in said anode compartment and an aqueous catholyte in said cathode compartment, both said catholyte and anolyte being maintained substantially free of dissolved oxygen gas, having a pH less than about 7.5, and being about 1-14 molar with respect to water soluble ammonium halide salt ot water soluble halide salt of a metal which is more electropositive than copper; said impure metallic copper containing a second metal which is in the metallic state;   b. electrochemically converting impure metallic copper in said anode into complex ions containing copper in the cuprous state, whereby copper in said anode passes into said anolyte as said complex ions by the action of electrodissolution, said converting step being accompanied by the transfer, from said alloyed metallic copper to said electrical circuit means, of about 1.0 faraday of electricity for each gram atom of copper converted to said complex ion;   c. excluding access of oxygen gas to said aqueous anolyte, whereby the copper in said cuprous state in said complex ions is maintained in said cuprous state, at least in said anolyte;   d. transferring copper-containing ions obtained in said anolyte to said catholyte;   e. electrochemically converting said copper-containing ions to substantially pure metallic copper at said cathode by consuming from about 1.0 to about 2.0 faradays of electricity for each gram atom of copper obtained; and   f. recovering the substantially pure metallic copper obtained by said step (e).   
     
     
       2. A method according to claim 1 wherein said anolyte is circulated to said cathode compartment to commingle with said catholyte. 
     
     
       3. A method according to claim 2 wherein said anolyte is passed through a purification zone before being circulated to said cathode compartment. 
     
     
       4. A method according to claim 2 wherein said anolyte is passed through a controlled oxidation zone prior to being circulated to said cathode compartment. 
     
     
       5. A method according to claim 1 wherein said anolyte and catholyte are essentially chemically identical fluids which are in electrolyte contact through an ion-permeable dividing medium. 
     
     
       6. A method according to claim 2 wherein said catholyte is circulated back to said anode compartment. 
     
     
       7. A method according to claim 1 wherein said impure metallic copper comprises 1-98% by weight metallic copper, and wherein said electrolytic cell is operated at a temperature of 15°-95°C. 
     
     
       8. A method according to claim 7 wherein said impure metallic copper is an alloy of copper and at least a second metal which is more electropositive than copper. 
     
     
       9. A method according to claim 1 wherein said substantially pure metallic copper obtained from said cathode, without any further refinement or purification, is greater than 99% by weight pure copper. 
     
     
       10. A method according to claim 1 wherein the aqueous electrolyte is mechanically stirred by continuous circulation through an electrolyte re-circulating system from which air is excluded. 
     
     
       11. A method according to claim 1 wherein said anolyte contains chloride ion in a concentration of at least 3.25 molar. 
     
     
       12. A method according to claim 1 wherein said impure metallic copper is an alloy of copper and at least a second metal which is more noble than copper, and wherein the more noble metal is recovered from said anode compartment. 
     
     
       13. A method according to claim 1 wherein said water soluble ammonium halide salt or water soluble halide salt of a metal which is more electropositive than copper is selected from the group consisting of chloride and bromide. 
     
     
       14. A method for hydrometallurgical recovery of metallic copper from alloy scrap containing alloyed metallic copper and at least a second metal, said method comprising the steps of: a. using said alloy scrap as the anode in an electrolytic cell containing a cathode, an external electrical circuit means for connecting said cathode to the resulting alloy scrap anode, and an aqueous electrolyte in contact with both said alloy scrap anode and said cathode, said aqueous electrolyte being maintained substantially free of dissolved oxygen gas, having a pH less than about 7, and being about 1.0-14 molar with respect to water soluble ammonium halide or a halide salt of a metal which is more electropositive than copper;   b. electrochemically converting alloyed copper in said alloy scrap, at said alloy scrap anode, into water soluble complex ions containing copper in the cuprous state, whereby said copper in said alloy scrap is introduced into said aqueous electrolyte as said water soluble complex ions through the action of electrodissolution, said converting step being accompanied by the transfer, from said alloyed metallic copper to said electrical circuit means, of about 1.0 faraday of electricity for each gram atom of copper converted to said complex ion;   c. preventing access of oxygen gas to said aqueous electrolyte during said step (b), whereby the copper in said cuprous state in said complex ions is maintained in said cuprous state;   d. circulating said water soluble complex ions produced in step (b) by agitation of said aqueous electrolyte to provide continual motion of aqueous electrolyte containing said water soluble complex ions at least in the region of said electrolyte surrounding said cathode and said anode;   e. electrochemically converting copper-containing ions resulting from step (b) to substantially pure metallic copper at said cathode by consuming about 1.0 faraday of electricity for each gram atom of copper obtained; and   f. recovering the substantially pure metallic copper obtained by said step (e).   
     
     
       15. A method according to claim 14 wherein said second metal is a metal which is more electropositive than copper. 
     
     
       16. A method according to claim 14 wherein said second metal is zinc. 
     
     
       17. A method according to claim 12 wherein said second metal is more noble than copper. 
     
     
       18. A process according to claim 14 wherein said water soluble ammonium halide or halide salt of a metal which is more electropositive than copper is selected from the group consisting of chloride and bromide. 
     
     
       19. A method for hydrometallurgical recovery of copper from alloy scrap containing metallic copper alloyed with metallic zinc, said method comprising the steps of: a. providing an electrolytic cell comprising: i. said alloy scrap as the anode;   ii. a 1.25-10 molar excess over stoichiometry of aqueous halide ion as the anolyte for said electrochemical cell, said anolyte being substantially free of dissolved oxygen gas and cupric ion and having a pH ranging from 0 to 7.0;   iii. a cathode in contact with a catholyte, said catholyte being in electrolyte contact with said anolyte;   iv. an external electrical circuit connecting said cathode to said anode;     b. under chemically non-oxidizing conditions, electrochemically converting metallic copper in said anode to a dissolved aqueous ionic copper (I) halide complex by electrodissolution, accompanied by the transfer, from said metallic copper to said external electrical circuit of about 1.0 faraday of electricity for each equivalent of copper (I) obtained thereby, said dissolved aqueous ionic copper (I) halide being dissolved in said anolyte;   c. simultaneously with said step (b), electrochemically converting metallic zinc in said anode to zinc cations, accompanied by the transfer, from said metallic zinc to said external electrical circuit, of about 2.0 faradays of electricity for each equivalent of zinc cation obtained thereby:   d. conveying said dissolved aqueous ionic copper (I) halide to said catholyte, thereby introducing dissolved copper values into said catholyte;   e. maintaining the copper of said ionic copper (I) halide complex in the copper (I) state by exclusion of atmospheric oxygen from said anolyte and said catholyte;   f. electrochemically converting said dissolved copper values in said catholyte to metallic copper of at least about 99 weight % purity;   g. repeatedly removing said metallic copper of at least about 99 weight % purity from said electrolytic cell and repeatedly adding more alloy scrap containing metallic copper to said anode; and   h. circulating said catholyte back to said anode for re-use as anolyte.   
     
     
       20. A process according to claim 15 wherein said acqueous halide ion is selected from the group consisting of chloride and bromide.